Endura WS5000 recording schedules fail to execute at the specified start and end times

Product Line

Pelco Video Management

Environment

SM5000 All versions

Pelco cameras and encoders, all versions

Endura NSM5200 Network Video Recorder, all versions

Endura DVR5300 Digital Video Recorder, all versions

Endura NVR5100 Network Video Recorder, all versions

Cause

This white paper explains Endura's basic principles, benefits, and considerations regarding accurate time keeping via the Network Time Protocol (NTP). It is intended for anyone interested in the basics of the how Endura manages the time settings using the NTP to keep all network devices within acceptable time difference tolerances and why it is an important part of any surveillance system. Furthermore the value added to the customers operations should become readily apparent by the end of this document.

Resolution

Section 1: Abstract

Section 2: Introduction

Section 3: Why Timekeeping is Critical

Section 4: What is Network Time Protocol (NTP)?

Section 5: Timekeeping with Endura

Section 6: Endura NTP Timekeeping In Detail

Section 7: Acceptable NTP Time Variation Range Diagram

Section 8: Conclusion

Abstract

This white paper explains Endura's basic principles, benefits, and considerations regarding accurate time keeping via the Network Time Protocol (NTP). It is intended for anyone interested in the basics of the how Endura manages the time settings using the NTP to keep all network devices within acceptable time difference tolerances and why it is an important part of any surveillance system. Furthermore the value added to the customers operations should become readily apparent by the end of this document. Accurate time keeping must be an essential part of any surveillance system. The methods of operation and terminology relevant to this important Endura feature and how the NTP protocol is incorporated will be explained.

Introduction

Endura offers a limitless platform for designing and implementing video security systems, enabling the system and its components to interact and share video, audio, and control information in any way specified by the particular installation requirements. A variety of procedures and protocols have been implemented to seamlessly integrate these functions. One of the most important protocols implemented into Endura through the System Manager component is the Network Time Protocol (NTP).

Why Timekeeping is Critical

Every electronic device, due to inherent design constraints, has a differential between the actual frequency of a clock and what the frequency should be to keep perfect time. This difference is known as "skew" and is measured in hertz. How quickly the skew of a clock is changing is called "drift" and is measured in hertz per second. All devices skew and drift at various rates. Slew, or slewing, is the term used to gradually adjust the time of a clock until it tells the correct time. In an Endura system, clock skew describes the difference in time shown by the clocks at the different nodes on the network. It is usually an unavoidable phenomenon (at least if one looks at millisecond resolutions), but clock skew of tens of minutes or more is also quite common. Even the smallest errors in keeping time can significantly accumulate over a long period of time. For example, if you have two clocks synchronized at the beginning of the year, but one consistently requires an additional 0.04 milliseconds to increment by one second, by the end of year one a difference of more than 20 minutes will have accumulated. While this may seem inconsequential, a deviation by only one-one hundred thousandth of a second will lead to the loss of almost a full second per day. In mission-critical distributed video surveillance systems, accuracy, authenticity, and video integrity are key to providing meaningful and legally admissible recordings. Verifiably accurate date and time stamps provide a reliable and simple way to help maintain each of those characteristics. A number of protocols have been designed to reduce clock skew, and produce more stable functions. The Endura system employs the Network Time Protocol.

What is Network Time Protocol (NTP)?

The Network Time Protocol (NTP) is a series of procedures for accurately synchronizing time between a server and its clients. The NTP service provides accurate time and date settings for use with the mission critical devices on a network. NTP was chosen for use in Endura due to it being an open industry standard. While other options were considered, NTP provided the strongest advantages with a minimum amount of limitations. These limitations include the fact that the date and time accuracy are only as good as the server providing them. If the server is incorrect for any reason then consequently all clients dependent on that server will be incorrect as well. By utilizing an external NTP time source to synchronize the SM5000 with periodically this risk can be mitigated completely.

Ordinarily a device sets its clock to the correct time with no intermediate adjustments, or slewing, via NTP. Step, or stepping, is the term used for a clock set to the correct time with no intermediate adjustments. However when it comes to a video surveillance system or other time accuracy critical system, setting the clock using step method will result in the perceived loss of video and inconsistent database information at a minimum. In order to alleviate this problem NTP allows for a clock to gradually adjust the time until it tells the correct time. This method adjustment of is known as "slewing".

Timekeeping with Endura

The Endura system relies on accurate time and date settings for a number of components. From a client perspective the most important reason to have accurate date and time settings is the ability to synchronize playback to a specific interval. Without synchronized time, playback of meaningful video would be very difficult. With a distributed system such as Endura all cameras and network devices must have accurate and synchronized time regardless of its location or distance from the SM5000. Additionally, as video gets written to a hard drive or other storage medium consistency must be maintained across all devices and operations. Lastly, in order to have scripts and alarms function as designed, the SM5000 must have accurate time and date settings or numerous problems will result. NTP allows all network devices to remain synchronized with a minimum amount of effort.

While NTP is a simple service, several options that must be carefully considered when it comes to obtaining and maintaining synchronized time setting across the network. The use of NTP with Endura can be implemented into either an open or a closed network with advantages and disadvantages to each discussed below. The security and network integrity necessary for each installation will dictate which installation is correct for your application.

With an Internet accessible, or open, network the Endura System Manager’s NTP server can be configured to automatically keep the date and time accurate to within 10–100 ms, depending on network conditions. This ensures very accurate date and time settings but is less secure than using a completely closed network. This method is also less expensive compared to a closed network because you can use existing Internet connected infrastructure as opposed to dedicating a separate closed Endura network. After an Endura System Manager’s NTP server has been successfully set up on your local network, all other devices on the network simply need to be configured to periodically verify the correct time and date. Setting the time server IP address in the WS5050 Software can do this. No further effort on the network devices is required after they have been configured. However, several issues must be considered for proper time synchronization. It is important to understand that when an SM5000 is the designated NTP server it requires between 5 and 10 minutes for the NTP service to analyze the local clock and begin providing the best accuracy. During this setup time, the SM will not be able to process time requests from any network clients. Once the NTP has started processing time requests, adjustments are performed at a minimum of once every 17 minutes or so and a maximum of once every 64 seconds.

At present, Pelco officially supports two methods of NTP synchronization:

Open Network (Internet Time Source)

Closed Network

The second option, and the one most attractive to the majority Pelco clients is a closed network. While offering the best security available, in tandem with a GPS or CDMA source, a solid, safe, accurate system can be easily maintained under a closed network. Within a closed network, careful attention must be paid to ensure accuracy of the Endura system’s time. Without a connection to the Internet, alternate methods must be designed. These methods can include specifying an internal (non-internet accessible) installation wide NTP server. It is strongly encouraged that most clients utilize the GPS or CDMA option to achieve the highest time precision.

Endura NTP Timekeeping In Detail

The Endura System Manager module is a mandatory component of any Endura installation. Endura System Manager modules function as an NTP server as well as performing other duties. Administrators can specify the NTP server of their choice if the default is not acceptable. What makes Endura unique and differentiates it from other surveillance systems available in the marketplace is its ability to deal with both large and small deviations.

Upon establishing a baseline time, the Pelco NTP Daemon will monitor for a difference of +/- 60 seconds from that of the NTP server. A daemon is a process that runs in the background and performs a specified operation at predefined times or in response to certain events. As long as the deviation is within 60 seconds, the normal operation of NTP will keep the time settings accurate. If a difference is found to be outside the 60-second threshold, the Pelco NTP Daemon will stop the local NTP client daemon and slew to the NTP server time at a rate of 1 second per 10 seconds as necessary. Once the offset between the system and the NTP server is within 1 second, the script will stop slewing the local clock and start the local NTP client daemon to begin keeping time again through the normal NTP operation. If a deviation of greater than 3600 seconds is detected, the Pelco NTP Daemon will initiate a reboot of the Endura Device.

In surveillance systems it is very important to employ the slew method of adjustment to ensure continuous video recording and data consistency while obtaining the correct time settings. If the system was to step the clock after getting an initial baseline there will be a large segment of time missing in the recordings, between what was considered the correct time and the actual step set time, and a resynchronization would have to be performed. Actual data, while not technically lost, would be very difficult to accurately find, retrieve, and may or may not have correct time and date settings. It’s important to realize a minor variation in the time settings of various network devices is not a concern. The Endura System Manager NTP server will adjust each device as necessary when it checks in at the specified interval. A diagram representing the maximum allowable drift range is shown below.

Acceptable NTP Time Variation Range Diagram

Endura System & Time Keeping with NTP (NTP)

Any value outside the gray area, representing a value too far ahead or too far behind the NTP server time, results in the Endura SM shutting down the local NTP client daemon and slewing the time as necessary until it is once again within the acceptable threshold represented in the gray area. Once this value is reached the Endura SM restarts the local NTP client daemon.

Conclusion

Endura, and specifically the System Manager component, provides tremendous flexibility and functionality for the surveillance system. It is imperative that Pelco staff and customers alike understand what, how, and why it performs as it does. Pelco has done everything within its power to minimize issues the customer may experience. NTP is an open standard that has been as carefully implemented as possible. With that in mind, NTP does have innate limitations, and where possible Pelco has engineered the products around these limitations. When properly understood and implemented, the Endura System Manager coupled with NTP ensure accurate time settings, avoiding confusion and any recording time inconsistency, while enhancing legal admissibility and video integrity.

Copyright 2006 Pelco. All Rights Reserved

This document is provided for information purposes only, and the contents hereof are subject to change without notice. This document is not warranted to be error-free, nor is it subject to any other warranties or conditions, whether expressed orally or implied in law, including implied warranties and conditions of merchantability or fitness for a particular purpose. We specifically disclaim any liability with respect to this document and no contractual obligations are formed either directly or indirectly by this document. This document may not be reproduced or transmitted in any form or by any means, electronic, mechanical, for any purpose without prior written permission from Pelco.